Thermionic cathode X-ray stabilizer system



April 1934- A. MUTSCHELLER 1,953,889

THERMIONIC CATHODE X-RAY STABILIZER SYSTEM Filed Sept. 23, 1931uuumHHHHH lTWENTOR HAW/M? #0715024? 5/? ATTORNEY til Patented Apr. 3,1934 UNITED STATES ATENT OFFE THERMIONIC CATHODE X-RAY STABILIZER SYSTEMof New York Application September 23, 1931, Serial No. 564,514

15 Claims.

My invention relates to X-ray systems and has particular relation tosuch a system wherein the current flowing through the X-ray tube, whichis conventionally termed the discharge current, is maintained constantunder all conditions of operation of the X-ray tube regardless of thetime period of energization of the latter.

In X--ray systems when it is desired to energize the X-ray tube withrelatively high milliamperage current the current utilized to heat thethermionic cathode of the X-ray tube or valve tubes employed forrectification purposes is comparatively high and must be maintainedconstant in order to maintain the discharge current constant. As thelow-tension transformer for heating the cathode and the high tensiontransformer for supplying the discharge current are usually connected toa common source of alternating current of commercial potential, thedrawing of a heavy current by the primary winding of the high tensiontransformer causes a voltage drop in the source which likewise causes adrop in the cathode heating current. It naturally follows that a drop inthe cathode heating current aiiects the discharge current, due to adecrease in electron emissivity of the thermionic cathode, which resultsin a lesser X-ray output from the Xray tube. 7

Various systems and methods for counteracting this variation of currentare known to the prior art, such for example, as a phase changingstabilizer or a synchronously operated short cirsuiting device in whichthe time of short circuiting is controlled by the tube current.

The first mentioned system, namely, the phase changing stabilizeroperates on the principle of the counter-action of the current suppliedfrom a closely coupled transformer against the current supplied from aloosely coupled transformer which results in the stabilization of theresulting current. These devices, however, operate with a very low powerfactor and depend upon over saturation of a magnetic core for theloosely coupled transformer and are, therefore, subject to thedeleterious effects of overheating or are lacking in a high degree ofpermanency.

In the systems wherein a synchronously operated short circuiting deviceis employed a portion of the heating current impulses are shortcircuited inversely in proportion to the desired cathode temperature.This enables the cathode to be heated to its maximum temperature andgreatest electron emission before the X-ray tube is energized. A coil isusually utilized which is connected in the high'tension dischargecircuit for operating the short circuiting contactor and the time periodof short circuiting is increased to bring the cathode emissivity to thatnecessary to give the desired milliamperage value. The variations of thecurrent in the discharge circuit are thus compensated for by variationsin the time periods of short circuiting the cathode heating circuitwhich reduces the temperature and electron emissivity of the cathode.

In this manner a stabilization of the cathode heating current isobtained but in such systems an appreciable time must elapse after shortcircuiting the cathode heating current before the cathode coolssufficiently to reduce the electron emissivity from maximum to theemissivity required to give the desired milliamperage of dischargecurrent.

Under normal operating conditions this cooling of the cathode to theusual operating value requires approximately one-tenth of a second whichis lost to the actual exposure period. It, therefore, follows that withexposures of less than onetenth of a second duration devices of thisgeneral type are not feasible.

It is accordingly an object of my invention to provide a system forenergizing an X-ray tube wherein the discharge current flowing throughthe tube is maintained constant.

Another object of my invention is the provision of a system forenergizing an X-ray tube wherein the discharge current flowing throughthe tube is maintained constant under all conditions regardless of thetime period of energization of said tube.

Another object of my invention is the provision of a system forenergizing an X-ray tube wherein the desired amount of energizationcurrents may be preset and this current maintained constant during theentire period of energization regardless of the length of the timeperiod during which the tube remains energized.

Another object of inventionis the provision of a system for energizingan X-ray tube wherein a compensating load is connected to the source ofenergy for the X-ray tube, corresponding to the load of the tube, andwhich is automatically removed from the source upon connection of theX-raytube thereto.

Another object of my invention is the provision of a system forenergizing an X-ray tube wherein a compensating load is normally imposedupon the source of energy for the tube, equivalent to theload of theX-ray tube which is automatically removed therefrom upon connection ofthe tube thereto to prevent current fluctuations in the source normallyattendant the connection of the tube to the source.

A further object of my invention is the provision of a system forenergizing an l-ray tube wherein the discharge current is maintainedconstant by presetting the amount of cathode heating current andmaintaining this amount constant under all operating conditions byvarying the same inversely to fluctuations in the source of supply.

Still further objects of my invention will become apparent to thoseskilled in the art by reference to the accompanying drawing wherein:

Figure 1 is a diagrammatical representation of an X-ray circuit forenergizing an X-ray tube showing the system employing the features of mypresent invention, and

Figure 2 is a diagramrnatical representation of the same systemdisclosed in Figure 1 with an additional feature for maintaining thedischarge current constant irrespective of supply source fluctuations.

Referring now to the drawing in detail I have shown in Fig. 1 a suitablesource of alternating current of commercial potential, such as theconductors L1 and L2. A high tension transformer 5, which is utilizedfor supplying currents of high potential to an X-ray tube 6, has itsprimary winding 7 connected to the source of supply L1, L2 by means of apair of conductors 8 and 9, and a switch 10 is provided for opening andclosing this circuit. A low tension transformer 11 is provided forsupplying heating currents to an audion tube 12, the latter beingemployed for a purpose to be hereinafter more fully stated, and theprimary winding 13 of this transformer is also connected to the supplysource L1, L2 by means of a pair of conductors l4 and 15.

A second low tension transformer 16 has its primary winding 17 likewiseconnected to the source of supply L1, L2 by means of a pair ofconductors 18 and 19. A ballast resistance 20 is interposed in theconductor 19 and is in series with the primary winding 17 and the sourceof supply for limiting the current supplied to the former. Thistransformer 16 is provided with a secondary winding 22 which isconnected to the cathode 23 of X-ray tube 6 for supplying heatingcurrents to the latter, by means of a pair of conductors 24 and 25.

An ammeter 26 is connected in series with the conductor 24 for recordingthe current supplied to the cathode 23 and may be graduated in terms ofmilliamperes.

The high tension transformer 5 has one end of its secondary winding 27connected to the anode 28, of the X-ray tube 6, by means of a conductor29 and the other end of this secondary winding is connected, by means ofa conductor 30, to the conductor 25 for completing the high tensioncircuit. A resistance 32, having a sliding contactor 33, is interposedin the conductor 30 for a purpose hereinafter set forth, and amilliampere meter 34 is likewise in series with the high tension circuitfor recording the current flowing through the circuit.

The low-tension transformer 11 has its secondary winding 35 connected tothe cathode 36 of the audion tube 12 by means of a pair of conductors3'7 and 38. The grid 39 of this audion is connected to the slidingcontactor 33 of the resistance 32, by means of a conductor 40, for thepurpose of applying a negative potential thereto during operation of thesystem.

The low-tension transformer 16 is provided with a compensating winding42 the greater portion of which constitutes an auxiliary load upon thistransformer and one end of this winding is connected, by means of aconductor 43, to the conductor 30 at the positive end of the resistance32. This same end of the auxiliary winding 42 is connected through aconductor 44 to the conductor 37 and thus to the cathode 36 of theaudion 12.

This winding 42 has a total output potential of approximately 1000 voltsand a conductor 45 connects the greater portion of this winding with theplate 46 of the audion 12. The remaining portion of the secondarywinding 42, which is arranged for an output potential of approximately100 volts, is short circuited by means of a conductor 47 across avariable rheostat 48.

A milliampere meter 49 may be interposed, if desired, in the conductor45 for recording the plate current supplied to the audion 12 althoughthis meter is not essential and the high tension discharge circuit maybe suitably grounded, as at 50, for safety purposes. The rheostat 48 isutilized to regulate the current flowing through the entire auxiliarywinding 42 and consequently the audion 12. The ballast resistance 20cooperates with this rheostat 48 in limiting the current flowing throughthe winding 42. The primary purpose of the inclusion of the ballastresistance 20 is to limit the size of the rheostat 48. By increasing thesize of the rheostat 48 to that required to give the proper regulationover a predetermined range of current the ballast resistance 20 may bedispensed with, if desired.

The circuit shown in Fig. 2 differs from that shown in the figure justdescribed in that a second audion tube is included in the system. Thepurpose of the audion 12 is to allow a current to flow through theauxiliary winding 42, that is equivalent to the drop in current in thesource of supply attendant the energization of the high tensiontransformer 5, thus constituting a compensating load which isautomatically shut oif from the source when current flows in thedischarge circuit. On the other hand the provision of the audion 55compensates for variations from other causes normally found in the usualcommercial source of supply.

A low tension transformer 56 has its primary winding 57 connected to thesource L1 and L2, by means of a pair of conductors 58 and 59. Thesecondary winding 60 of this transformer is connected to the cathode 62of this audion 55, by means of a pair of conductors 63 and 64, for thepurpose of supplying heating current thereto.

In this modification the conductor 47, which extends from one end of theauxiliary winding 42, is connected to the cathode 62 and the plate 65 isconnected, by means of a conductor 66, to the adjustable arm of rheostat48. The filament or cathode 62 and plate 55 are thus in series with aportion of the secondary winding 42. A conductor 67 connects theconductor 4'7 with the supply conductor L2 and the grid 68 is connected,by means of a conductor 69, to the other supply conductor L1, at one endof the ballast resistance 20.

In this manner a slight potential is applied between the grid 68 and thecathode 62 with the grid, due to the characteristics of the audion 55,being normally supplied with a predetermined potential. A current willflow under normal con ditions between the cathode 62 and plate 65without any choking effect by the grid 68. When, however, the currentrises in the source of supply due to any cause the grid 68 allows thefiow of current between the cathode and plate to likewise increase inthe well known manner of opera-- tion of audion tubes, and has the sameeffect as that of decreasing the resistance within the circuit by meansof the rheostat 48. In all other respects the system shown in Figure 2is identical with the system shown in Figure 1.

In the operation of my system a suitable switch (not shown) in thesupply source L1, L2 is first closed thereby energizing the primarywindings 1'7 and 13 of the transformers 16 and 11. The secondary winding22 thus becomes energized to heat the cathode 23 of X-ray tube 6 and thesecondary winding 35 of transformer 11 becomes energized to heat thecathode 36 of audion 12. Upon energization of transformer 16 theauxiliary winding 42 is likewise energized and permits a current to flowthrough this winding and be tween the cathode or filament 36 and plate46 of audion 12. This circuit may be traced from one end of winding 42,through conductor 44 to the cathode 36, then to the plate 46, throughmilliammeter 49, conductor 45, rheostat 48 and conductor 47 back to thewinding 42. A portion of the current flowing in this circuit will fiowthrough conductor 45 to the intermediate point of the secondary winding42 but the majority of the current will flow through the rheostat 48 andthe entire winding 42.

The greater portion of winding 42 between the points of connection ofthe conductors 43, 45 is of a capacity within the range of drop involtage or in other words causes a potential drop in the source L1, L2equivalent to that resulting in the source of supply attendant theenergization of the high tension transformer 5, and the current isregulated by means of the rheostat 48 to give the desired amount offilament heating current for the cathode 23 of X-ray tube 6. The ballastresistance 20 is selected to give a current within a short range of thedesired cathode heating current or between approximately 3 and 5 amperesand further adjustment of the cathode is made by rheostat 48.

As the winding 42 is wound upon the same core of transformer 16 as thewinding 22, which supplies heating current to the cathode 23, increasingthe current in the winding 42 by means of the rheostat 48 causes adecrease in the current in the winding 22 and consequently in thecathode heating current. Conversely a decrease in current in the winding42 by regulation of the rheostat 48 causes a simultaneous increase ofcurrent in the winding 22 and cathode 23.

The rheostat 48 is therefore adjusted until the ammeter 26 records theamount of cathode heating current desired and the milliampere meter 49will record the milliamperage of plate current i of the audion 12. Ifdesired, the milliammeter 49 may be proportioned to record the,milliamperage of the X-ray tube. As an increase of current in thewinding 42 follows an increase of plate current, which is recorded bythe milliamrneter 49 and a decrease in cathode heating current occurs,there would likewise follow, upon energization of "the high tensiontransformer 5, a decrease in the milliamperage of discharge current.

In a like manner a decrease in plate current through audion 12, byregulation of the rheostat with an attendant increase in cathode heatingcurrent would result in an increase in the milliamperage a in thedischarge circuit of the X-ray tube. The

reading of milliammeter 49 is, therefore, inversely proportional to themilliamperage of the discharge circuit and may be calibrated to rec-0rdthe amount of current desired in this circuit when the high tensiontransformer is energized.

The sliding contactor 33 of rheostat 32 is adjusted and the switch 10 isclosed to energize the primary winding 7 of high tension transformer 5.This will in turn cause the secondary winding 27 to energize the X-raytube 6 with high potential electrical energy during positive half wavesof the alternating current cycle with the X-ray tube acting as arectifier thus suppressing the flow of current through the highpotential or discharge circuit during the remaining or negative halfwaves of the cycle. This high potential or discharge circuit may betraced from one end of the secondary winding 27, through conductor 30and rheostat 32, milliammeter 34, conductor 25 to cathode 23 of X-raytube 6, and from anode 28 thereof through conductor 29 to the other endof secondary winding 27.

If the setting up of the sliding contactor 33 is such that an increaseor drop in cathode heating current, as recorded by the ammeter 26,occurs upon energization of the high tension transformer this rheostatis adjusted until no variation of the meter 26 occurs upon energizationof the transformer. This rheostat 32 is initially set once for existingline and wiring conditions and need not be further disturbed.Immediately upon energization of the high tension transformer and theflow of current in the high tension or discharge circuit a negativepotential is applied to the grid 39 of audion 12 by means of theconductor 40.

As this latter conductor is connected to the adjustable arm 33 ofrheostat 32, which is naturally negative with reference to the positiveend of this rheostat the grid is consequently impressed with a negativepotential. lhe cathode 36 of audion 12, being connectedto the positiveend of rheostat 32 through conductors 43 and 44, is impressed with apositive potential relative to the grid 39 with the result that thepassage of electrons from the cathode 36 to the plate 46 is prevented.

, In applying a negative potential to the grid the current which wasflowing through the auxiliary Winding 42 in the manner previouslydescribed is automatically shut off by the action of the audion instopping the flow of electrons between the cathode 36 and plate 46. Theload or current consumed by the greater portion of secondary winding 42is thus simultaneously removed from the source of supply L1, L2 with theenergization of the high tension transformer, and the drawing of currentfrom the source, which causes the milliamrneter 49 to drop to zero.

As the system has been properly adjusted by the regulation of therheostats 48 and 32 the discharge current remains uniform and there isno variation in the filament heating current when the load of the hightension transformer is connected to the source.

When, the switch 16 is again opened to de energize the high tensiontransformer 5 the current flowing in the discharge circuit immediatelyceases. This removes the negative potential from the grid 39 which againenables a current to how between the cathode and 46 of audion 12 and theload of the awriliary winding 42 is again applied to the transformer 16.The system is again in condition for energizing of the X-ray tuhewithout a drop in the source normally a tendant the energization of thehigh tension transformer.

In the modification of my system shown in Figure 2 the operation of thesystem is identical with that just described with the additional featureof compensating for supply source variations resulting from othercauses. The audion tube 55 has its grid 68 connected to the supplyconductor L1 by means of conductor 69 and the filamentary cathode 62 isconnected to the supply conductor L2 by means of conductors 67 and 47. Apotential is, therefore, applied between the grid and cathode whichcorresponds to the potential of the source L1, L2. This potential,however, due to the characteristics of the audion 55 is insufiicient toprevent the fiow of electrons between the plate and cathode 62 duringthe normal operation of the system. As the cathode 62 is connected toone end of the auxiliary winding 42, by means of the conductor 47, andthe plate 65 is connected to the arm of rheostat '48 these electrodesare in series with the rheostat 48 and a portion of the winding 42.

The potential impressed upon the grid 68 from the source Ll, throughconductor 69, is such that an increase in the potential of the sourcecauses an increased flow of energy through the audion 55, between thecathode 62 and plate 65, and a decrease of the potential of the sourceL1, L2 causes a diminution of the energy flowing between the cathode 62and plate 65. This action of audion 55 causes an identical action in therheostat 48, i. e., upon a decrease flow of energy through the former adecrease follows in the series connected rheostat 48 and vice versa.

Moreover, as the rheostat 48 efiects the flow of energy through theremainder of the winding 42 and audion 12, an increase or decrease ofenergy through rheostat 48 has the same effect as increasing ordecreasing the energy through this latter circuit in the same manner asthough the rheostat 48 was manually adjusted as previously described.This naturally causes an increase or decrease in the energy supplied bythe winding 22 to the cathode 23 of the X-ray tube 6 inversely to thechange of energy flowing through winding 42 in the manner statedrelative to Fig. 1. It, therefore, becomes obvious that audion 55functions with supply source fluctuations to increase or decrease theloading on the winding 42 of trans former 16 and cause inversefluctuations in the secondary winding 22 of this transformer.

When the high tension transformer 5 is energized a negative potential isimpressed upon the grid 39 of audion 12 to prevent the flow of energythrough the greater portion of the winding 42 in the same manner asdescribed relative to Fig. 1 and in all other respects the operation ofthis latter modification is identical with the former.

It can thus be readily appreciated by those skilled in the art that Ihave provided a system for energizing an X-ray tube wherein acompensating load is normally applied to the source of supply for theX-ray tube that corresponds to the drop in the source of supplyattendant the energization of the X-ray tube. This compensating load issimultaneously disconnected from the source upon energization of thetube from the latter to thereby prevent a drop in potential of thesource and to maintain the cathode heating temperature constant.Furthermore my system compensates for supply source variations resultingfrom extrinsic causes and maintains the temperature of the cathode anddischarge current constant under all conditions.

Although I have shown and described several embodiments of my inventionI do not desire to be limited thereto as various other modifications ofthe same may be made Without departing from the spirit and scope of theappended claims.

What is claimed is:

1. In a system for energizing a thermionic cathode discharge device,means for supplying heating current to the cathodeof said device, hightension means for supplying electrical energy to said device, a sourceof electrical energy for energizing both of said means and subject to adrop in potential upon connection of said high tension means thereto,and compensating means connected to said first mentioned means andcausing a drop of potential in said source equivalent to the drop ofpotential therein attendant the connection of said high tension meansthereto, said compensating means including a device associated with saidhigh tension means to cause said compensating means to becomenon-conductive upon energization of said discharge device.

2. In a system for energizing a thermionic cathode discharge device,means for supplying heating current to the cathode of said device, hightension means for supplying electrical energy to said device, a sourceof electrical energy for energizing both of said means and subject to adrop in potential upon connection of said high tension means thereto,and compensating means connected to said first mentioned means andcausing a drop of potential in said source equivalent to the drop ofpotential therein attendant the connection of said high tension meansthereto, said compensating means including a device associated with saidhigh tension means to cause said compensating means to becomenon-conductive and. remove the potential drop in said source attendantenergization of said compensating means, upon connection of said hightension means to said source with attendant drop of potential therein.

3. In an X-ray system, an X-ray tube having a cathode to be heated, alow tension transformer for supplying heating current to the cathode ofsaid X-ray tube, a high tension transformer for energizing said X-raytube, a source of electrical energy for energizing both of saidtransformers and subject to a drop in potential upon connection of saidhigh tension transformer thereto, a compensating load connected to saidlow tension transformer and causing a drop of potential in said sourceequivalent to the drop of potential in said source attendant theconnection of said high tension transformer thereto, said compensatingmeans including a device operably connected to said high tensiontransformer to cause said compensating load to become non-conductive andremove the potential drop from said source attendant energizationthereof, simultaneously with the connection of said high tensiontransformer to said source with an attendant drop of potential in thelatter.

4. In an X-ray system, an X-ray tube having a cathode to be heated, alow tension transformer for supplying heating current to the cathode ofsaid X-ray tube, a high tension transformer for energizing said X-raytube, a source of electrical energy for energizing both of saidtransformers subject to a drop in potential upon connection of said hightension transformer thereto, and means lconstituting a compensating loadenergizable by said source and causing a potential drop in the latter tocompensate for the drop of potential in said source attendant theconnection of said high tension transformer thereto, said compensatingload including means operably connected to said high tension transformerto cause said compensating load to become non-conductive and effectthereof removed from said source upon connection of said high tensiontransformer to said sour'ce'to prevent a drop in potential fromoccurring in the latter and thereby maintaining the current supplied tothe cathode of said X-ray tube constant.

5. In an Xray system, an X-ray tube having a cathode to be heated, a lowtension transformer for supplying heating current to the cathode of saidX-ray tube, a high tension transformer for energizing said X-ray tube, asource of electrical energy for energizing both of said transformers andsubject to a drop in potential upon connection of said high tensiontransformer thereto, and means comprising a compensating load connectedto said low tension transformer and causing a potential drop in saidsource equivalent to the drop of potential therein attendant theconnection of said high tension transformer to said source, saidcompensating load including means connected with said high tensiontransformer to cause said compensating load to become non-conductive andthe effect thereof to be removed from said low tension transformer andsaid source upon energization of said high tension transformer.

6. In an X-ray system, an X-ray tube provided with a cathode to beheated, an electrical circuit for supplying heating current to thecathode of said X-ray tube, a high tension circuit for supplying energyto said X-ray tube, a source of electrical energy common to both of saidcircuits and subject to a drop in potential upon energization of saidhigh tension circuit, and means constituting a compensating load circuitoperably connected with said source of energy for causing a potentialdrop therein equivalent to the drop of potential in said sourceattendant energization of said high tension circuit, said compensatingload circuit including means connected to said high tension circuit tosimultaneously cause said cornpensating load circuit to becomenon-conductive and remove the effect thereof from said source uponapplication of the load of said high tension circuit thereto.

T1. In an X-ray system, an X-ray tube provided with a cathode to beheated, a transformer connected with said cathode in order to heat thesame by supplying current thereto, a high tension transformer forenergizing said X-ray tube, a source of electrical energy common to bothof said transformers for supplying exciting currents thereto,

and a compensating load circuit connected to said first mentionedtransformer and energized thereby constituting a load which causes apotential drop in said source equivalent to the drop of potential insaid source attendant the energization of said last mentionedtransformer, said compensating load circuit including a discharge deviceassociated with said last mentioned transformer and X-ray tube, tosimultaneously render said compensating load circuit non-conductive andremove the effect thereof from said first mentioned transformer and saidsource, upon energization of said high tension transformer.

8. In an X-ray system, an X-ray tube having a cathode to be heated, atransformer provided with a plurality of secondary windings one of whichis connected to the cathode of said X-ray tube for supplying heatingcurrent thereto and the other being connected to a discharge device andconstituting a compensating load circuit, a igh tension transformer forsupplying high potential energy to said X-ray tube, a source ofelectrical energy common to both of said transformers and subject to adrop in potential upon energization of said high tension transformer,

and regulating means in said compensating load circuit to adjust thelatter and cause a potential drop in said source equivalent to the dropof potential therein following energization of said high tensiontransformer, said discharge device in the compensating load circuitbeing operably connected to said high tension transformer and X-ray tubeto open said compensating load circuit and remove the load thereof fromsaid source simultaneously with the energization of said high tensiontransformer from said source.

9. In an X-ray system, an X-ray tube having a cathode to be heated, alow tension transformer for supplying heating current to the oathode ofsaid X-ray tube, a high tension transformer for energizing said X-raytube, a source of electrical energy for energizing both of saidtransformers subject to a drop in potential upon energization of saidhigh tension transformer from said source, a compensating loadassociated with said low tension transformer and causing a potentialdrop in said source equivalent to the drop of potential in said sourceattendant the connection of said high tension transformer thereto, andadjustable means connected with said compensating load to vary theenergy supplied by said low tension transformer thereto, and to vary theenergy supplied to said cathode inversely to the variations of energysupplied to said compensating load, said compensating load including athree electrode tube connected to said high tension transformer to causesaid compensating load to become non-conductive and remove the effectthereof from said 10w tension transformer and consequently fromsaidsource, upon the connection of said high tension transformer to saidsource.

10 In an X-ray system, an X-ray tube having a cathode to be heated, alow tension transformer for supplying heating current to the cathode ofsaid X-ray tube, a high tension transformer for energizing said X-raytube, a source of electrical energy for energizing both of saidtransformers and subject to a drop in potential upon connection of saidhigh tension transformer thereto, and a compensating load connected tosaid low tension transformer and causing a potential drop in said sourceequivalent to the drop of potential therein attendant the connection ofsaid high tension transformer to said source, said compensating loadincluding a three electrode tube having two of its electrodes connectedto said compensating load and the third electrode connected with saidhigh tension transformer to cause said compensating load to becomenon-conductive and remove the effect thereof from said low tensiontransformer and consequently from said source, upon the energization ofsaid high tension transformer from said source.

11. In an X-ray system, an X-ray tube having a cathode to be heated, alow tension transformer for supplying heating current to the oathode ofsaid X-ray tube, a high tension transformer for energizing said X-raytube, a source of electrical energy for energizing both of saidtransformers and subject to a drop in potential upon the connectionthereto of the load of said high tension transformer, and a compensatingload associated with said source and normally energized thereby andcausing a potential drop in said source equivalent to the drop ofpotential therein attendant the connection of the load of loads fromsaid source upon the application of the other of said loads thereto, toprevent a drop of potential in said source and to thereby maintain thecathode heating current constant.

12. In an X-ray system, an X-ray tube having a cathode to be heated, a10W tension transformer for supplying heating current to the cathode ofsaid X-ray tube, a high tension transformer for energizing said X-raytube, a source of electrical energy for energizing both of saidtransformers subject to a drop in potential upon connection thereto ofthe load of said high tension transformer, and a compensating loadassociated with said source and causing a drop of potential thereinequivalent to the drop of potential in said source attendant connectionof said high tension transformer thereto, said compensating loadincluding a three electrode tube having two of its electrodes connectedto said compensating load and the remaining electrode connected to saidhigh tension transformer to cause said compensating load to becomenon-conductive and remove the effect thereof from said source uponconnection of the load of said high tension transformer thereto, andsaid three electrode tube being operable to cause said compensating loadto become conductive and cause a drop of potential in said source upondisconnection of the load of said high tension transformer therefrom toprevent a variation of potential in said source whereby the supply ofcurrent to the cathode of said X-ray tube is maintained constant.

13. In an X-ray system, an X-ray tube provided with a cathode to beheated, a low tension transformer for supplying heating current to thecathode of said X-ray tube, a high tension transformer for energizingsaid X-ray tube, a source of commercial electrical energy subject tonormal potential fluctuations for energizing both of said transformersand subject to a drop in potential upon connection of said high tensiontransformer thereto, a compensating load connected to said source andcausing a potential drop therein equivalent to the drop of potential insaid source attendant the energization of said high tension transformer,and means connected to said compensating load and to said source forvarying the energy supplied to said compensating load upon theoccurrence of normal fluctuations in said source, said compensating loadbeing connected 14. In an X-ray system, an X-ray tube provided with acathode to be heated, a low tension transformer for supplying heatingcurrent to said cathode, a high tension transformer for energizing saidX-ray tube, a source of electrical energy for energizing both of saidtransformers and subject to variations caused by extrinsic forces andalso subject to a drop in potential upon connection of said high tensiontransformer thereto, a compensating load connected to said source andcausing a potential drop therein equivalent to the drop of potential insaid source attendant the energization of said high tension transformer,m ans connected to said compensating load and to said source for varyingthe energy supplied to said compensating load upon the occurrence ofnormal fluctuations in said source to maintain the heating currentsupplied to said cathode constant, said compensating load includingmeans connected to said high tension transformer to in stantaneouslycause said compensating load to become non-conductive and remove theeffect thereof from said source upon the connection of said high tensiontransformer thereto to prevent a variation in said source and tomaintain said cathode heating current constant.

15. In an X-ray system, an X-ray tube provided With a cathode to beheated, a low tension transformer for supplying heating current to saidcathode, a high tension transformer for energizing said X-ray tube, asource of electrical energy for energizing both of said transformers andsubject to variations caused by extrinsic forces and also subject to adrop in potential upon connection of said high tension transformerthereto, a compensating load connected to said source and causing apotential drop therein equivalent to the drop of potential in saidsource attendant the energization of said high tension transformer, anda three electrode tube connected to said compensating load and to saidsource for varying the energy supplied to said compensating load uponthe occurrence of normal fluctuations in said source to maintain theheating current supplied to said cathode constant, said compensatingload including a second three electrode tube connected to said hightension transformer to instantaneously cause said compensating load tobecome non-conductive and remove the effect thereof from said sourceupon the connection of said high tension transformer thereto to preventa variation in said source and to maintain said cathode heating currentconstant.

ARTHUR MUTSCHELLER.

